This application claims the priority of German Patent Document 198 60 253.7, filed Dec. 24, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a membrane module of the stacked plate type for selective gas separation.
Such a membrane module for selective hydrogen separation is described in Offenlegungsschrift EP 0 718 031 A1. In that membrane module, the separating units form hydrogen-permeable composite membranes that consist of a support matrix covered on both sides with a selectively hydrogen-permeable metal layer with the interposition of a flexible intermediate layer. The support matrix contains a hydrogen absorbing structure able to carry away the separated hydrogen since it is formed of a porous, perforated, or slotted metal or ceramic material or a hydrogen-permeable metal material. To remove the separated hydrogen from the plate stack, laterally discharging hydrogen outlets are provided perpendicular to the stacking direction at a lateral area of the stack. Corresponding purging gas inlets leading laterally into the support matrix are provided on the opposite side of the stack. The composite membrane units alternate in the stack with frame plates which, with the interposition of gaskets, are in contact with the composite membrane units and their interior is completely open and in this manner form a gas mixture flow chamber. By means of a corresponding connecting and binding structure on the two lateral areas at which the purging gas inlets and the hydrogen outlets are located, a guided flow of gas mixture is achieved, in which the gas mixture containing the hydrogen is carried (1) from one end of the stack into the lateral area of a first frame plate, from there through its gas mixture flow chamber to the opposite lateral area, and (2) with a 180.degree. turn to the next frame plate and through its gas mixture flow chamber. This continues until the gas mixture, free of hydrogen, is carried out from the opposite end of the stack. This serpentine course of the gas mixture, however, involves corresponding losses of pressure.
In U.S. Pat. No. 5,486,475 a membrane module of the stacked plate type is disclosed, in which a plurality of membrane pocket units are stacked one over the other. The units consist of a frame plate which is surrounded top and bottom by a gas-permeable, liquid-proof membrane, so that pockets are formed in the interior through which a mixture of fluid can flow, by which undesired gases, which are to be separated from a gas mixture, can be reacted. The frame plates are provided with inlet openings and, in an opposite lateral area, with outlet openings, in order to introduce the mixture into the pockets and take them out again. Between each two membrane pocket units, spacers are placed in opposite stack side areas, so that corresponding chambers are formed between the individual membrane pocket units, into which a supporting structure can be inserted and into which the gas mixture is introduced. The spacers are perforated such that a distribution channel is formed at the two corresponding stack side areas running parallel to the stacking direction, and a collecting channel is formed in order to carry the liquid mixture parallel into the membrane pockets and carry it away again.
Hydrogen separating membrane modules are used, for example, in fuel-cell vehicles for the purpose of selectively separating the hydrogen produced by a reforming reaction of a hydrocarbon or hydrocarbon derivative from the reformate gas mixture in order to feed it to the fuel cells. For such mobile applications in automotive technology it is desirable, for dynamic and space reasons, to make the hydrogen-separating membrane module as compact and light as possible. Therefore the membrane area per unit volume should be maximized. At the same time, the flow management must be considered. In particular, high pressure losses should be avoided because they impair the performance of the membrane module. This impairment is because the separating power depends directly on the pressure gradient between the gas mixture flowing through the membrane module and the gas separated therefrom. In addition, the membrane module must withstand high pressures in a hydrogen atmosphere at temperature up to at least 350.degree. C., and it should be able to be manufactured at low cost.
The object of the invention is the preparation of a membrane module of the stacked plate type that can be manufactured with a given, separating power in a compact, light, and pressure-stable form with relatively little expense, and which will cause relatively little pressure loss in operation.
This object is achieved by a membrane module according to the present invention. Due to the modular construction of the stacked plate type, the membrane module can be designed very flexibly for various separating powers. The stacked plate construction also permits low-cost manufacture. Through connecting openings appropriately placed into the separating units and in the frame plates in lateral areas, connecting passage structures running in the stacking direction are formed for the input and removal of the gas mixture, as well as for the removal of the separating gas (i.e., the gas selectively removed from the gas mixture). Through these connecting passage structures, the gas mixture can be fed in parallel, with relatively little loss of pressure, through the chambers through which the gas mixture flows, and the separated gas can be withdrawn from the separating units. At the same time, the integration of the connecting passage structures in the plate stacks permits a compact design.
A membrane module embodied according to another embodiment of the present invention contains a rectangular plate stack in which the gas mixture is carried through the stack parallel to the longer side of the rectangle. The separated gas is carried away in a transverse direction through the shorter side of the rectangle. Thus, on the one hand the length of the flow of the gas mixture, which is necessary for sufficient separation, can be achieved, while the stack can be kept shorter in the transverse direction perpendicular thereto, which contributes to a compact structure and low pressure losses.
In another embodiment of the present invention, the support plate of each separating unit has on one or both sides a pattern of grooves and lands in which the grooves form passages for removing the separated gas. A gas separating membrane in each case is laid onto the groove-and-wall structure with an interposed porous supporting structure. The membrane is thus sufficiently supported, and the gas selectively separated by it can pass uniformly into the grooves and be carried away from there.
In another embodiment according to the present invention, the gas-separating membrane, together with an interposed supporting structure if any, is disposed in a recess in the adjacent frame plate. Thus, when the membrane module plate stack is assembled it can be held securely in the frame plate recess. In addition, this creates the possibility of manufacturing the support plate at relatively low expense as a flat component into which a separating gas receiving structure is created on one or both sides.
In a membrane module according to another embodiment, metal materials are selected for the different components of the plate stack such that the components can be assembled gas-tight in a single soldering or welding process. This reduces the manufacturing cost.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.